Type of base malt will certainly make some difference. I've never used Maris Otter myself, but hear nothing but good about it.
Your mash schedule is also very important. Higher temps (up to 158, as opposed to 150) will leave you with more unfermentable sugars, thus giving a fuller body and sweeter, maltier flavor. I notice a difference even from a couple of degrees change in mash temp.
For more extreme maltiness, some people recommend a decoction mash. Others claim this is a waste of time and makes no flavor difference. I have yet to try this myself (I've always just used an infusion mash) but am planning to attempt a decoction for my next-but-one brew to see if I notice any difference.
Finally, other kinds of grain will all provide different malty flavors. Crystal, Vienna, Munich, Honey, Aromatic, can all contribute some pretty in-your-face malt flavors. But they're all different, plus different from the style of maltiness you get from a pale base malt with a high mash temp. "malty" is actually a pretty broad term encompassing many different flavors!
So it all depends on what you are going for. Are there any particular commercial brews that you're trying to mimic? That would help us narrow down the best way to get there.